Bathing facilities have taken various forms. Large indoor, heated pools date from antiquity. In Roman times families and social groups gathered at the baths. Soaking in the warm water was a significant part of the experience, but it was principally a social activity. In more recent years, smaller bathtubs have been provided for the purpose of bathing with soap to clean the body. With this function in mind, they were configured for the purpose of cleanliness and included the changing of the water. The smaller size is compatible with the changing of the water after each bath.
The hot tub has found resurgence in recent years as a social meeting place, with mutual soaking in a larger hot water-containing tub, without changing the water. Since the tub was larger, it usually has been placed outdoors. As a consequence, the outdoor hot tub has been provided with shelter from sun and wind. During non-use, such an outdoor hot tub has a cover to keep windblown contaminants from entering the water and to save the heat in the water. Sometimes these outdoor hot tubs are called “spas” after a town in eastern Belgium which has mineral baths. For many years, such a natural mineral bath was believed to have therapeutic effects. The modern hot tub usually does not have significant mineral content. The hot tub took advantage of the fact that resting in warm water is soothing and restful. Modern bathtubs combine the cleanliness of changing the water with the soothing pleasure of resting in the warm water filled tub.